Reference

Heat builds up in the tablet device and the AC adapter while the tablet device is in use or being charged.

    Heat buildup while the tablet device is in use or being charged is normal and should not affect the performance of your tablet device.
    The tablet device may shut down for safety when overheated. If this happens, use the tablet device in a cool area until it cools down.
    If your tablet device becomes abnormally hot, it may be in need of repair. Turn off your tablet device, and stop using the the AC adapter and tablet device. Contact the service/support center named in the warranty.